The proposed research program will continue studies to characterize the mechanism by which a collagenous matrix derived from beef tendon induces the formation of a matrix bound form of hydroxyapatite. This reaction will occur in systems that have Ca plus 2 and HPO-2 sub 4 concentrations identical to or lower than those of physiological fluids. The reaction is stimulated by fluoride and inhibited by Sr plus 2, tetracycline, diphosphonate compounds that similarly influence calcification reactions in vivo. This investigation has the potential of elucidating mechanisms that might apply to in vivo systems. We have also demonstrated the existence of serum and erythrocyte components that inhibit matrix calcification. The concentration of the inhibitor inside the erythrocyte is approximately 50 times that of serum. We propose to characterize the structure of these inhibitors and to study physiological factors such as pH, PCO2, temperature, etc. that might influence their distribution between extracellular and intracellular phases. We also propose to determine if an energy linked transport system controls this distribution and whether this occurs with soft tissues as well. We also intend to study the distribution of these inhibitors between serum and erythrocytes obtained from normal, anephric, and transplant subjects in an effort to determine a correlation between the distribution of these substances and physiological states that are manifested by altered serum calcium and phosphate levels, osteodystrophy, and metastatic calcification of soft tissue.